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    <TITLE>package org.opengis.filter</TITLE>
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    Filters {@linkplain org.opengis.feature.Feature features} according their properties.
    A <CITE>filter expression</CITE> is a construct used to constraints the property
    values of an object type for the purpose of identifying a subset of object instances
    to be operated upon in some manner.
    <p>
    The following is adapted from the <a href="http://www.opengeospatial.org/standards/filter">OpenGIS&reg;
    Filter Encoding Implementation Specification</a>:
    <ul>
    <li><a href="http://portal.opengeospatial.org/files/?artifact_id=1171">02-059 1.0 Filter Encoding</a>
    <li><a href="http://portal.opengeospatial.org/files/?artifact_id=1171">04-095 1.1 Filter Encoding Implementation Specification</a>
    </ul>

    <H3>Comparison operators</H3>
    <P ALIGN="justify">A comparison operator is used to form expressions that evaluate
    the mathematical comparison between two arguments. If the arguments satisfy the comparison
    then the expression {@linkplain org.opengis.filter.Filter#evaluate evaluates} to {@code true}.
    Otherwise the expression evaluates to {@code false}.</P>

    <P ALIGN="justify">In addition to the standard set
    ({@code =},{@code <},{@code >},{@code >=},{@code <=},{@code <>}) of comparison operators,
    this package defines the elements {@link org.opengis.filter.PropertyIsLike},
    {@link org.opengis.filter.PropertyIsBetween} and {@link org.opengis.filter.PropertyIsNull}.</P>

    <H3>Logical operators</H3>
    <P ALIGN="justify">A logical operator can be used to combine one or more conditional expressions.
    The logical operator {@link org.opengis.filter.And} evaluates to {@code true} if all the combined
    expressions evaluate to {@code true}. The operator {@link org.opengis.filter.Or} operator evaluates
    to {@code true} is any of the combined expressions evaluate to {@code true}. The
    {@link org.opengis.filter.Not} operator reverses the logical value of an expression.
    The elements {@code And}, {@code Or} and {@code Not} can be used to combine scalar,
    spatial and other logical expressions to form more complex compound expressions.</P>
    
    <H3>Identity</H3>
    <P ALIGN="justify">Identity can be checked using {@link org.opengis.filter.Id}, selected objects
    will are matched against a set of {@link org.opengis.filter.identiy.Identifier}.</p>
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